This invention relates to an internal combustion engine and more particularly to an improved control system and method for such engines.
In order to improve engine transitional performance particularly when going from idle to off idle and mid-range, it has been proposed to provide a system wherein the throttle valve is maintained in a more fully open position than normal when the accelerator pedal or throttle control is in its idle condition. By keeping the throttle valve more fully open, air flow can more easily increase in velocity when engine speed increases are called for.
Since the throttle valve is held more fully open at idle than required to supply the engine's air flow requirements at idle, some other arrangement is provided for controlling the engine speed and/or power output during the time period when the throttle is more open than the throttle control position would dictate. For example and as shown in co-pending application Ser. No. 08/299,517, entitled "Combustion Control System For Internal Combustion Engine", filed Sep. 1, 1994 (SANSH2.671A) and assigned to the assignee hereof, there is disclosed an arrangement wherein the appropriate idle speed is maintained by disabling the firing of one or more cylinders. Hence, in the time interval when the operator throttle control moves from its idle position until the throttle valve is more fully open, engine speed is controlled by a means other than by controlling the throttle valve position.
This system, although highly effective, controls the engine speed and/or power output by selectively disabling a number of cylinders. The cylinders are disabled by either cutting off fuel supply and/or cutting off firing of the spark plugs although effective this is cumbersome and can present other problems.
It is, therefore, a principal object of this invention to provide an improved control system and method for an internal combustion engine.
It is yet further an object of this invention to provide an arrangement where the throttle valve may be left in a substantial partially open position at idle and off idle and the speed and/or power may be controlled in another manner.
Another running condition of the engine which is quite critical is initial warm up. When a cold engine is first started, it is generally necessary to provide a richer than normal fuel air ratio. This is done so as to compensate for the condensation or lack of total vaporization of the fuel supplied to the engine. Obviously this is an undesirable running condition and various arrangements have been proposed for assisting in more rapid warm up of the engine.
For example, it is the common practice to operate the engine at a faster than normal speed or racing of the engine during initial warm up. By running the engine faster than normal then the engine will reach an operating temperature sooner. However, this has a disadvantage in that excess fuel consumption results.
In addition, when the engine speed is increased, the spark advance is increased and the fuel supply amount is even further increased. Hence, the engine operates in such a way as to consume more fuel but also do it in a generally more efficient manner that reduces the likelihood of rapid warm up or alternatively does not warm the engine up as fast as possible considering the amount of fuel consumed.
It is well known to vary the spark timing of an engine in response to running characteristics. Generally the firing of the spark plug should be at such a time that the peak pressure in the combustion chamber occurs at some time shortly after top dead center position of the piston. In this way, the maximum amount of energy expanded by the combustion products can be converted into the rotational power of the out engine output shaft.
However and in accordance with an embodiment of this invention the combustion is operated in the combustion chamber in such a way so as to rather than increase the output or rotational speed of the engine, the actual energy created by the burning of the fuel is employed to heat the engine. That is, instead of moving the spark timing to the optimum for the running condition, the spark timing is adjusted so that the maximum pressure in the combustion chamber will occur well after the time that the piston has passed top dead center position. By doing this the heat of the expansion of the gases will not necessarily be transferred into increased power of the engine but rather the heat generated will be transferred to the combustion chamber walls and absorbed as heat energy therein. As a result, the engine will be heated more rapidly and the increased fuel consumption is more directly transferred into a rise in the engine operating temperature rather than increased engine output.